Mark fast/events/platform-wheelevent-paging-x-in-scrolling-div.html as flaky

TBR=apotapchuk@chromium.org

Bug: 1047176
Change-Id: Ic25a9fcde0a23cdc488ab86c1ab52837d9616b72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2139898Reviewed-by: Chris Sharp <csharp@chromium.org>
Commit-Queue: Chris Sharp <csharp@chromium.org>
Auto-Submit: Chris Sharp <csharp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757065}

third_party/blink/web_tests/TestExpectations

@@ -6592,6 +6592,7 @@ crbug.com/1065335 [ Win ] fast/hidpi/image-srcset-relative-svg-canvas.html [ Pas
 crbug.com/1065335 [ Win ] fast/hidpi/image-srcset-relative-svg-canvas-2x.html [ Pass Failure ]
 # Sheriff 2020-04-01
 crbug.com/1066122 virtual/threaded-no-composited-antialiasing/animations/events/animation-iteration-event.html [ Pass Failure ]
+crbug.com/1066732 fast/events/platform-wheelevent-paging-x-in-scrolling-div.html [ Pass Failure ]
 crbug.com/1066732 fast/events/platform-wheelevent-paging-y-in-scrolling-div.html [ Pass Failure ]
 # Sheriff 2020-04-02
 crbug.com/1067084 virtual/paint-timing/external/wpt/paint-timing/fcp-only/fcp-with-rtl.html [ Pass Failure ]